reading an O2 sensor | LabJack

reading an O2 sensor

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CharlieMason's picture
reading an O2 sensor


I've a galvanic cell to measure oxygen concentration. The datasheet attched says it makes 80 to 120 uA at 20.9% O2. It says use a load from 47 to 100 ohm. I've tried various connections to my LJ T4 and got the most stable reading thus far by connecting it single ended across a 250 ohm resistor. So that's the cell and 2 x 500 ohm resistors all connected parallel gnd to AIN. I multiply reading by 700 to get roughly 20.9% O2. I haven't any 100% O2 handy at moment so I can't easily check for linear readings yet. The reading dips as expected when I breath on the sensor.

I'm wondering what you'd expect to be best way to connect to LJ T4 for most stable readings? I'm not getting as stable a reading as I've seen in off-the-shelf O2 concentration sensors which use similar galvanic cell. This cell alone reads 0.66V with my DMM.

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labjack support's picture
If they say 100 ohm is the

If they say 100 ohm is the max load I would stick with that.  Seems that this sensor is magically producing power (P=R*I^2) so it would make sense to not go over the max recommended resistor.

I don't see anything about the max current output across O2 range, but the max at 20.9% appears to be 120uA.  With 100 ohms of resistance that is only 12 mV.

The resolution of a high voltage analog input on the T4 is about 5 mV, and the resolution of a low voltage input is about 600 uV.  So FIO4 to EIO3 will do better than AIN0-3, but still probably not good enough.  You likely need an LJTick-InAmp or move up to the U6 or T7 to get better resolution.